1. Field of the Invention
This invention relates to fuel systems for internal combustion engines and is directed more particularly to a device for cooling a fuel pump and fuel in a fuel system of a marine internal combustion engine.
2. Description of the Prior Art
It is known that an internal combustion fuel system subject to high temperatures will experience "vapor lock" when the fuel reaches the temperature at which the fuel vaporizes. It is further known that fuel pumps, typically with tight tolerance between rotor and housing, expand under high temperature operations, expanding the space between rotor and housing, leading to inefficiency in operation. Still higher temperatures are known to cause the flashing of vapor in the pump which is designed to operate only with the liquid fuel.
In the automotive industry, the fuel pump frequently is placed in the fuel tank, stabilizing the temperature of the pump and fuel therein. However, in marine applications it is required by the Coast Guard that fuel pumps be no more than twelve inches from the engine, eliminating the fuel tank from consideration as a cool place in which to locate the fuel pump. The fuel pump thus absorbs heat from engine surfaces and from the ambient environment, leading to unduly high temperatures, causing the aforementioned vaporization of fuel in the pump and/or system and a marked reduction in fuel pump efficiency. The likelihood of fuel vaporization is increased in marine applications by the known fact that fuel vaporizes at a substantially lower temperature when placed under a negative pressure, as when pulled from a fuel tank by a fuel pump external to the tank, than when placed under a positive pressure provided by a fuel pump inside the fuel tank.
Aggravating the above scenario is the fact that a marine fuel system must be able to idle indefinitely and in the idling state, the fuel temperature rise is greatest. This is because more of the fuel is unused fuel recycled through a fuel recycle line to the system from the engine, with relatively little cool "new" fuel being added. Further, even after shut down of the system, for the first hour, or so, the temperatures in the bilge climb, subjecting fuel lines and the fuel pump to increased heat, often causing vapor lock conditions and a "non start" situation when restart of the engine is sought.
There is thus a need for a device which stabilizes the temperature of the fuel pump and fuel therein, and cools the fuel in the fuel recycle line, thereby cooling the fuel in the system generally so as to maintain the fuel and the fuel pump in a relatively cool condition, below vaporization temperature of the fuel, and permitting the pump to operate continuously at high efficiency.